The use of proteases in animal feed, or to treat vegetable proteins, is known from the following documents:
WO95/28850 discloses i.a. an animal feed additive comprising a phytase and a proteolytic enzyme. Various proteolytic enzymes are specified at p. 7.
WO96/05739 discloses an enzyme feed additive comprising xylanase and a protease. Suitable proteases are listed at p. 25.
WO95/02044 discloses i.a. proteases derived from Aspergillus aculeatus, as well as the use in animal feed thereof.
U.S. Pat. No. 3,966,971 discloses a process of obtaining protein from a vegetable protein source by treatment with an acid phytase and optionally a proteolytic enzyme. Suitable proteases are specified in column 2.
U.S. Pat. Nos. 4,073,884, 5,047,240, 3,868,448, 3,823,072, and 3,683,069 describe protease preparations derived from various strains of Streptomyces and their use in animal feed.
These proteases, however, are not acid-stable and/or are not proteases of the subtilisin family.